This invention relates to tool inserts.
Tool inserts which consist of an abrasive compact bonded to a cemented carbide substrate are known in the art and are used extensively in tools such as mining picks, cutting tools and drill bits. The abrasive compact may be a diamond or cubic boron nitride abrasive compact. Such tool inserts have been extensively described in the patent literature, for example in British Patent No. 1,489,130 and U.S. Pat. Nos. 3,745,623 and 3,743,489.
British Patent No. 2,146,058 describes a cutting tool for a mining machine which comprises a holding lug, one end of which is adapted for mounting in a working surface of the machine, and the other end of which is provided with a socket, and a cutting insert located in the socket and secured to the lug. The cutting insert comprises an essentially hemispherical abrasive compact bonded to a cemented carbide substrate. The hemispherical shape abrasive compact provides a curved cutting edge for the cutting tool. In an alternative embodiment, the cutting insert comprises a cemented carbide substrate having a curved hemispherical end to which is bonded a thin skin of abrasive compact. Cutting inserts of the type described by this British patent, it has been found, give rise to stresses at the carbide/compact interface during brazing of the insert into the socket of the holding lug. South African Patent No. 84/0643 describes a tool insert which comprises a disc-shaped abrasive compact backed by cemented carbide and surrounded around at least 75% of its circumference by cemented carbide. The cutting edge is provided either by the cemented carbide or by an exposed edge of the abrasive compact.